1. Field of the Invention
This invention relates to a method of manufacturing an electronic part in which wiring layers are successively laminated on a core material, and an electronic part, and particularly to a method of manufacturing an electronic part which is suitable for forming an electrical conductor forming inter-layer connection in the wiring layers, and an electronic part.
2. Related Background Art
There is known an electronic part in which wiring layers are successively laminated on the surface of a core material, and connection is effected among these laminated wiring layers to thereby form stereoscopic wiring structure.
In the wiring layers, there have been proposed and disclosed various manufacturing methods for forming a conductor portion forming inter-layer connection. FIGS. 8A to 8D of the accompanying drawings are process illustrations showing the conventional manufacturing process of the wiring layer of an electronic part.
The wiring layer constituting the electronic part, as shown in FIG. 8A, has a base member 1 formed of an insulating material having a predetermined thickness, and lower layer wiring 2 formed on the back side of this base member 1 and in the interior of the base member 1.
To form a conductor portion 3 and upper layer wiring 4 (see FIG. 10 of the accompanying drawings for both) on the surface side of such a form of wiring layer, dry film 6 providing protective film is first attached to the surface side of the wiring layer on which copper foil 5 is generally formed. After the dry film 6 has been attached to the base member 1, as shown in FIG. 8B, exposure and a developing process are effected on the dry film 6 to thereby form an opening portion 7 in the formed area of the conductor portion 3. Thereafter, as shown in FIG. 8C, the copper foil exposed on the bottom surface of the opening portion 7 is removed by different etching to thereby expose the base member 1, and blast processing is effected on the surface of this exposed base member 1 to thereby expose the lower layer wiring 2 underlying the base member 1. FIG. 8D shows a state in which by the blast processing, the lower layer wiring 2 is exposed on the bottom surface of the opening portion 7.
Now, while in the above-described conventional example, aperture forming in the base member 1 is effected by blast processing, this method is not restrictive, but other method may also be used.
FIGS. 9A and 9B of the accompanying drawings are process illustrations showing the procedure of forming an opening portion by the use of laser working. FIG. 9A shows the state of a wiring layer before the laser working, and a laser working machine (not shown) for affecting the working of this wiring layer is disposed above this wiring layer.
By the use of a positioning mechanism provided in the laser working machine, a laser irradiating portion is moved to the predetermined forming position of the opening portion 7 to thereby individually effect the aperture forming work for the copper foil 5 and the base member 1. FIG. 9B shows the state after the opening portion 7 has been formed by laser working.
Usually, a YAG laser (yttrium aluminum garnet laser) is used for the above-described working of the copper foil 5, and a carbonic acid gas laser is used for the working of the base member 1 formed of insulating resin. These different lasers can be carried on one and the same positioning mechanism from the standpoint of an improvement in working efficiency so that continuous working (of the copper foil 5 and the base member 1) may be effected. Also, instead of the use of the YAG laser, only the copper foil may be subjected to patterning by etching.
After the opening portion 7 in which the lower layer wiring 2 is exposed on the surface of the wiring layer has been thus formed, this opening portion 7 is filled by a metal material to thereby form a conductor portion 3.
FIGS. 10A, 10B and 10C of the accompanying drawings are process illustrations showing the procedure of forming the conductor portion in the opening portion.
To form the conductor portion in the opening portion, as shown in FIG. 10A, electroless plating is first effected on the front side of the wiring layer in which the opening portion 7 is formed, with a view to improve the adhesiveness with the base member 1, to thereby form an electroless plating layer 8. After this electroless plating layer 8 has been formed, electroplating is effected with this electroless plating layer 8 as an electrode, and an electroplating layer 9 is precipitated on the upper layer of the electroless plating layer 8 so as to fill the opening portion 7. FIG. 10B shows the state after the electroplating layer 9 has been formed.
After the electroplating layer 9 has been thus formed, as shown in FIG. 10C, a conductor portion 3 and upper wiring 4 are formed on the copper foil 5, the electroless plating layer 8 and the electroplating layer 9 by the use of a subtractive method.
Now, while in the above-described conventional example, the electroless plating layer is used to improve the adhesiveness between the base member 1 and the conductor portion 3 (see, for example, Japanese Patent Application Laid-open No. H11-343593), there is also known a method of applying other processing in place of the electroless plating layer (see, for example, Japanese Patent Application Laid-open No. 2001-217553).
However, the use of the above-described electroless plating (and other method replacing the electroless plating) has posed such problems will be shown below.
When as shown in FIG. 10B, electroplating is effected to try to fill the opening portion 7 with a metal material after the electroless plating layer has been formed, the electroplating layer 9 is thickly formed on the whole of one side of the wiring layer and as the result, there has arisen the problem that when as shown in FIG. 10C, a wiring pattern is to be formed by etching, the cross section of this wiring pattern becomes trapezoid, and dimensional accuracy is reduced and a wiring pattern of a narrow width cannot be formed.
Also, when the electroless plating layer 8 is formed and electroplating is effected with this layer as an electrode, fresh plating liquid is more applied to the surface of this electroless plating layer 8 than to the inside of the aperture. Therefore, the growth of the electroplating layer 9 on this surface is promoted, and this has resulted in the possibility that before the opening portion 7 is filled with a metal material, the opening portion 7 is closed (by the electroplating layer 9) and a so-called void forms in the interior of the conductor portion 3.
Also, in a case where electroless plating is not used, but other ante-processing is effected, there has been the possibility that a similar problem may arise.
Now, when electroless plating is used, a metal catalyst is used to cause the plating to adhere also to other portion (insulator portion) than a conductor. However, if this metal catalyst is residual on the surface of a wiring layer, there has been the possibility that an insulation resistance value may be reduced or such trouble as the short-circuiting of a wiring pattern may be caused. In the electronic parts in recent years, a narrower pitch has been advanced and the possibility of the occurrence of the above-noted trouble has more increased.